2011 ASCE SEI Structures Congress April 16, 2011 - Las Vegas, Nevada Computational Analyses of Quasi-Isolated Bridges with Fusing Bearing Components Evgueni T. Filipov – Graduate Research Assistant , Department of Civil & Environmental Engineering (CEE), University of Illinois Jerome F. Hajjar – Professor, and Chair, CEE, Northeastern University Joshua S. Steelman – Graduate Research Assistant , CEE, University of Illinois Larry A. Fahnestock – Professor, CEE, University of Illinois James M. LaFave – Professor, CEE, University of Illinois Douglas A. Foutch – Professor Emeritus, CEE, University of Illinois Illinois Center Illinois Department for Transportation of Transportation
Introduction IDOT Earthquake Resisting System (ERS): Recently developed & adopted design approach tailored to typical Illinois bridge types (and in part addressing increased hazard levels in AASHTO) Primary objective: Prevention of span loss Three levels of design and performance: » Level 1: Connections between super- and sub-structures designed to provide a nominal fuse capacity » Level 2: Provide sufficient seat widths at substructures to allow for unrestrained superstructure motion » Level 3: Plastic deformations in substructure and foundation elements (where permitted) Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 2 Fusing Bearing Components
Quasi-Isolation for Bridges Typical bridge bearing systems designed to act as fuses to limit the forces transmitted from the superstructure to the substructure Type I bearings: bearings with an elastomer to concrete sliding surface Type II bearings: elastomeric bearings with PTFE sliding surface L-shaped retainers: designed to limit service load deflections Low-profile bearings with steel pintles and anchorbolts BRIDGE BEAM BRIDGE BEAM BRIDGE BEAM STEEL TOP PLATE TOP PLATE WITH POLISHED PINTLE STAINLESS STEEL SURFACE TYPE I ELASTOMERIC BEARING WITH STEEL PTFE SURFACE LOW-PROFILE FIXED SHIMS TYPE II ELASTOMERIC BEARING BEARING WITH STEEL SHIMS RETAINER ANCHOR BOLT RETAINER ANCHOR BOLT CONCRETE ANCHOR BOLT CONCRETE SUBSTRUCTURE CONCRETE SUBSTRUCTURE SUBSTRUCTURE Elastomeric bearing with Elastomeric bearing on concrete Low-profile fixed bearing PTFE sliding surface Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 3 Fusing Bearing Components
Bridge Prototype Model Three 50’ spans with six W27x84 Gr. 50 composite girders and 8” concrete deck 15’ Tall multi-column intermediate substructures Concrete abutments with backwalls and 2” gap from deck Pile foundations for all substructures 50'-0" 50'-0" 50'-0" Type I - Bearings 42'-0" Bridge Prototype Plan TYPE I - ISOLATION ABUTMENT BEARINGS W27x84 15'-0" LOW-PROFILE MULTI-COLUMN Low-profile fixed bearings FIXED BEARINGS PIER Mesh Representation of OpenSees Model Bridge Prototype Elevation Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 4 Fusing Bearing Components
Modeling of Bearing Components Sliding elastomeric bearing models Ongoing experimentation is studying behavior Difference in static vs. kinetic coefficient of friction Friction slip-stick behavior noted in cases 70 60 60 40 20 50 Force (kN) 0 Force (kN) 40 -20 Bearing Type I; Exp.#1 30 -40 Model: µ SI =0.37& µ K =0.29 20 -60 Bearing Type II; Exp.#9 -80 Bearing Type I; Exp.#5x1 10 Model: µ SI =0.14& µ K =0.06 Model: µ SI =0.35; µ SP =0.33; µ K =0.24 -100 0 0 50 100 150 200 -200 -100 0 100 200 Displacement (mm) Displacement (mm) Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 5 Fusing Bearing Components
Bi-directional bearing elements Dependent on axial force Allows for initial capacity and different pre and post-slip static coefficients of friction Force-displacement behavior coupled in orthogonal shear directions Kinematic-hardening surface used to trace bearing movement ( Δ X_ 1 , Δ Z_ 1 ) Z Δ FRIC_BREAK Δ SLIDE F SI + F INITIAL Combined θ 1 Δ Z_ 0 Force θ 0 + 2 2 Δ P_Z_ 0 F F F SP X _1 Z _1 F K E INITIAL Combined E FRIC Displacement Δ P_X_ 0 Δ X_ 0 X Static condition if Δ INITIAL Δ SLIDE Δ FRIC ∆ + ∆ 2 2 ( Δ X_ 1 , Δ Z_ 1 ) is within _1 _1 X Z BREAK BREAK dashed circle Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 6 Fusing Bearing Components
Modeling of Bearing Retainers Retainer simulation for System Analyses Gap with elasto-plastic response until retainer fracture Independent behavior of the (2) retainers Calibrated based on experiments and Finite Element Modeling p 140 Experiment # 7 120 Retainer Model 100 Force (kN) 80 60 40 20 0 0 10 20 30 40 50 60 70 Displacement (mm) Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 7 Fusing Bearing Components
Intermediate Substructures Beam-column elements with lumped plasticity at nodes Fiber sections used to model nonlinear behavior at hinge locations of column Nodes for bearing attachment to substructure 250 200 Linear elastic 150 pier cap 100 Force (KN) 50 Column pier 0 substructure with -50 lumped plasticity -100 at beam hinges -150 Uncracked -200 Cracked Elastic lp -250 Cracked Inelastic Linear elastic -0.1 -0.05 0 0.05 0.1 pile cap Top Node Displacement (m) Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 8 Fusing Bearing Components
Foundations and Backwalls Pile group analysis performed to Substructure develop nonlinear force-displacement Lateral Stiffness representation of foundations Rotational Stiffness Axial Hyperbolic gap material used to model Stiffness backwall interaction Hyperbolic Gap 5cm (2”) Gap Element Left Abutment Backwall element with Deck node 0cm(0”) gap Superstructure Force (KN) 5000 assembly 5cm (2") Rigid Link Expansion Gap representing backwall 0 -0.08 -0.07 -0.06 -0.05 -0.04 -0.03 -0.02 -0.01 0 Displacement (m) Right Abutment Backwall Zero length Node at bottom of bearing element allowing Zero length elements Force (KN) plastic hinge 0” 5000 representing bearing and capability of retainer connectivity 5cm (2") backwall Expansion Gap Node for local abutment 0 behavior 0 0.01 0.02 0.03 0.04 0.05 0.06 0.07 0.08 Displacement (m) Springs to model local abutment foundation Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 9 Fusing Bearing Components
Limit State Identification Longitudinal Bearings Elastomer deformation & nonlinear behavior Yielding and fracture in anchor bolts & pintles of fixed bearings Sliding of bearings on substructure Column and wall piers Cracking of concrete Yielding of reinforcement Crushing of concrete Foundations Plastic deformation of backwall & backfill Plastic deformation of pile groups & pile caps Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 10 Fusing Bearing Components
Longitudinal Analysis Limit state identification stiff foundation 2500 yr Paducah ground motion Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 11 Fusing Bearing Components
Longitudinal Analysis Slip of bearings at abutments Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 12 Fusing Bearing Components
Longitudinal Analysis Yielding in substructure #2, backwall interaction, and plastic deformation in foundation Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 13 Fusing Bearing Components
Longitudinal Analysis Slip of bearings at pier #1 Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 14 Fusing Bearing Components
Limit State Identification Transverse Bearings Elastomer deformation, retainer deformation with fracture & nonlinear bearing behavior Yielding and fracture in anchor bolts & pintles of fixed bearings Sliding of bearings on substructure Column and wall piers Cracking and/or crushing of concrete Yielding of reinforcement Foundations Plastic deformation of pile groups & pile caps Possible interaction with backwall & backfill Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 15 Fusing Bearing Components
Transverse Analysis Limit state identification fixed foundation 2500 yr Paducah ground motion (only 8 Seconds) Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 16 Fusing Bearing Components
Transverse Analysis Plasticity in retainers and bearing slip at abutment # 1 Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 17 Fusing Bearing Components
Transverse Analysis Fracture of retainer component Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 18 Fusing Bearing Components
Transverse Analysis Fracture of fixed bearing Computational Analyses of Quasi-Isolated Bridges with 04/14/2011 19 Fusing Bearing Components
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